Many semiconductor fabrication processes comprise one or more steps wherein a material is exposed to fluorine-containing species. The fluorine-containing species can be, for example, in the form of hydrogen fluoride. An example use of hydrogen fluoride in semiconductor fabrication processes is to strip silicon dioxide from a surface. Another example use of hydrogen fluoride is to passivate a silicon surface (i.e., to react hydrogen with dangling silicon bonds).
Passivation of silicon surfaces and/or stripping of silicon dioxide can be utilized to enhance formation of hemispherical grain (HSG) polysilicon. Example HSG polysilicon fabrication processes are described in U.S. Pat. Nos. 5,634,974 and 5,691,228, which are incorporated herein by reference. Generally, the fabrication processes disclosed in such patents comprise forming a layer of amorphous silicon, passivating and/or cleaning the layer of amorphous silicon with hydrofluoric acid, and converting the amorphous silicon to HSG polysilicon. A method of converting amorphous silicon to HSG polysilicon comprises seeding the amorphous silicon by, for example, irradiation or doping, to form nucleation centers for subsequent growth of individual grains of HSG polysilicon. HSG polysilicon is grown from the nucleation centers by annealing the seeded amorphous silicon at, for example, a temperature of from about 200.degree. C. to about 1500.degree. C. and a pressure of from about 1.times.10.sup.-8 Torr to about 1 atmosphere for a time of from about one second to about five hours.
The hydrofluoric acid treatments utilized in the above-described fabrication of HSG polysilicon either comprise an HF vapor clean, or a dip within an HF solution. If a dip is utilized, the temperature of the dip solution will be about 21.5.degree. C. The dip solution is generally kept within a vessel configured to cool the dip solution to maintain a temperature of about 21.5.degree. C. An advantage of the 21.5.degree. C. temperature is that it is a temperature which has traditionally been used for HF dipping, and accordingly there is a large amount of information available pertaining to appropriate dipping times and conditions for various applications. Another advantage is that the equipment presently manufactured for dipping within HF solutions is configured to maintain a temperature of about 21.5.degree. C. If the temperature were to vary significantly, it would introduce unwanted variability into a fabrication process.
It is desired to develop alternative methods of utilizing fluorine-containing species for treating materials during semiconductive fabrication processes.